Good question, and I don't know where to find the answer either. Keeping in mind that the U.S. involvement in WW1 aviation occurred late and on a small scale compared to European manufacturers, but there was cooperation among allies during the war.

I don't know how you could tell that a Paragon prop had been exported to the UK. I have never seen a Paragon with stampings that conformed to the British "style" of identification, but knowing that the American Propeller Manufacturing Company had produced 25,000 propellers by the end of the war, it's hard to imagine that some of them weren't exported.